LEDs are current-driven devices. LEDs are used in a various kinds of electronic applications such as architectural lighting, automotive head and tail lights, backlights for liquid crystal display devices including personal computers and high definition TVs, flashlights, etc. A LED driver circuit generally requires a constant direct current (DC), which is fed to a LED load. The LEDs have significant advantages such as high efficiency, good directionality, color stability, high reliability, long life time, small size, and environmental safety. The lumen output intensity (i.e. brightness) of the LED approximately varies in direct proportion to the current flowing through the LED. Thus, increasing current supplied to an LED increases the intensity of the LED and decreasing current supplied to the LED dims the LED. The current may be modified by either directly reducing the direct current level to the LEDs or by reducing the average current through duty cycle modulation. For power supply applications, such as a battery charger or light emitting diode (LED) ballast, the power supply should provide a constant current. If load resistance is above this value, the output voltage needs to be constant.
Various types of conventional driver circuits that regulate the primary side current are known in the prior art. The U.S. Pat. No. 7,525,259 B2 describes a primary side regulated power supply system with constant current output. The claimed power supply system has a primary side and a secondary side. An input terminal on the primary side is operable to receive an input voltage. An output terminal on the secondary side is operable to be connected to a load for providing current thereto. Circuitry is provided which is operable to regulate the power supply system from the primary side so that the current provided to the load at the output terminal is substantially constant.
The U.S. Pat. No. 9,083,252 B2 describes the primary-side regulation for isolated power supplies. The claimed DC-DC converter includes a primary side sense circuit to detect a load current of the DC-DC converter based on reflected current from a secondary winding of the DC-DC converter to a primary winding of the DC-DC converter. A primary side diode models effects of a secondary side diode that is driven from the secondary winding of the DC-DC converter. An output correction circuit controls a switching waveform to the primary winding of the DC-DC converter based on feedback from the primary side sense circuit and the primary side diode.
However, in the claimed systems, the secondary side current consumption information is galvanically isolated. Typically, the secondary side currents are regulated though the information provided to primary side by a link such as an opto-coupler. The use of an opto-coupler is an expensive approach and provides a weak link in the system to achieve accurate primary side regulation (PSR) in LED applications.
Typically, the conventional system uses an explicit Low pass filter (LPF) to correct the Peak Regulation Voltage (PRV) at the end of a half cycle for inherent filtering. Typically, the PRVs are corrected at multiple points within a half cycle using high correction frequency. The increase in correction frequency susceptible to high frequency errors or noises and needs adequate filtering in LED applications.
Hence, there is need for a system to achieve accurate primary side regulation. (PSR), Power Factor Correction (PFC), dimming functionality without the need of external components. Further, the method corrects the PRV of primary loop to meet desired half cycle reference voltage or current, which in turn achieves the desired secondary loop currents in LED circuit using a firmware.